This invention relates to a method for producing pulp from fibrous ligno-cellulose containing material, in which the pulp material, such as wood chips, is disintegrated in a grinding apparatus which comprises at least two opposing grinding discs which rotate relatively to one another under axial pressure within a housing. The material is introduced from a supply passage into the grinding space between the discs at the inner radial portion thereof and is propelled outwards in an atmosphere of steam or gas.
The supply passage usually includes a vessel in which the material to be ground is preheated by a heating medium, such as steam, under atmospheric or higher pressure, before it is fed into the grinding space.
It is known that the fiber pulp in this manner acquires favorable properties for production of paper and the like, namely, with regard to brightness and strength, if the grinding process is carried out at a temperature ranging between 100.degree. C. and 140.degree. C., preferably 118.degree. C.-125.degree. C., and at a corresponding steam pressure, since the treatment is of short duration and the concentration or dryness of the pulp is relatively high, such as 15%-40%. A further advantage with this so-called thermo-mechanical pulping method is that chemicals can be dispensed with to a substantial degree, which is important for environmental reasons, among others.